The Southern Subbasin includes the complete drainage area of the South Fork of Ten Mile River. This subbasin is contained within Mendocino County (Figure 1). The subbasin is characterized by a forested landscape of rugged, steep, sharp-crested ridges and narrow stream valleys. Stream elevations range from approximately 5 feet at its confluence with the mainstem of Ten Mile River to approximately 3,090 feet in its headwaters near Sherwood Peak. The subbasin encompasses about 39 square miles, occupying 32 percent of the total assessment basin area.

There are no towns within this subbasin. The Southern subbasin is mostly held by timber companies who manage it for timber production and in scattered private parcels commonly less than 40 acres, by ranchers and residences. Fish surveys of the streams in this basin have identified the presence of Coho, Steelhead, and Chinook salmon.

The climate of this subbasin is dominated by the coastal marine layer giving this area mild, foggy summers and wet winters.